Video transcript

All right, so you take a
little balloon, let's assume. You see it on the table, and
you can't resist yourself. You take that balloon. And you start to
think about how to do a little experiment with it. Maybe that's not
what you're thinking, but that's certainly what
you should be thinking, because we're going to
have a lot of fun checking out and learning about this
balloon by giving it some air. So imagine if you
put some pressure into that balloon,
what would happen? It would, of course,
get larger, right? So you know that the
volume of the balloon is going to go up as you put
pressure into that balloon. But you actually want to
measure it, let's say. So you go ahead and give a
small amount of pressure, maybe a small breath. And this balloon gets
a little bit bigger. And you note that a small amount
of pressure is over there, and it gets a little
bit bigger over there. So you put a little
x right there. Very good. Now, you go back and
give it a little bit more pressure, a little
bit bigger breaths. And you do the same thing. You say, well,
there's my pressure. And now it's a
little bit bigger, so I am going to put a
little x right there. And you do this again
with a large, large amount of pressure. And you notice the balloon
is getting much bigger now. So you figure out that as
you put in more pressure, the balloon is getting
bigger and on top of that, it's happening at a
linear rate, right? So the more pressure
you're putting in, you're getting a direct
amount of volume for that. Now, not all balloons are
going to behave this way. But let's assume,
for the moment, that this balloon does that. So it gets bigger and bigger
as you put more pressure. Great. This is my balloon. Now, you notice that there's
one more thing sitting on the table, and you grab it. And it's a plastic
wand, like this. And you dip it in soap, and you
make a balloon-- or, a bubble, rather. Not a balloon this time,
a bubble out of the soap. So you give it a soft breath,
just like you did before. And you notice that
even with a soft breath, you get kind of a large volume. So that's interesting, right? So kind of a large volume. And then you give it
a medium-sized breath. And you get even
a larger volume. Let's say, something like
this-- even a larger volume. And you can see where
this is going to go, because I'm going to
give it a large breath. And maybe it'll fill
out this entire corner, something like that. You get this enormous
bubble, and it doesn't burst, let's assume. So now you have three little
blue x's for the bubble, and you connect them
just as you did before. And this is my bubble line. And you can already see
something interesting, right? You can see that the
balloon has a smaller slope than the bubble. The bubble is
rising more quickly. And so thinking about this,
you could actually say, well, this is a formula
for the soap-- rise in volume over run, which would
be pressure, in this case. And if you do rise over
run, you get the slope. And in this case, we're going
to call the slope compliance-- really interesting
and important word. Seems pretty simple, right? It's just-- how
big does something get when you give it a
certain amount of pressure? And you can see, in this
case, that the bubble has more compliance
than the balloon. Good. So now we've figured
out a couple things, and I'm going to add one more
new word, which is actually just the inverse. What if I flipped it around? What if I put pressure over
here, and volume over here? I can do that, right? I can just take the same
data, the same information, and just flip the
two axes around. And if I did that,
then in this case, the balloon line
would be over here, something like that, right? Because all I'm doing
is just flipping the way we look at this chart. And the bubble line would be
over here, something like that. So now my bubble and my
balloon have switched places because the axes have switched. In a way, you could literally
just tilt the graph over, and you'd get the same thing. So there's nothing magical. But the thing that is
different about this is that now, if I'm calculating
rise over run, or the slope, I actually have flipped the
volume and pressure, right? So now my pressure is on top,
and the volume is down below. And if you have it like
this-- pressure over volume-- we actually call that elastance. So the first one, we
called compliance. And this one, we call elastance. And so you can see that
elastance and compliance are basically just inverses
of one another. They're just the
flip of one another. And so these two words,
you're going to hear them, but I want you to
see how they're very, very much the same
kind of thing. It's just that one is the
inverse of the other one. OK. So now we've gotten that. I'm going to make some
space here, like that. And I'm going to bring
up one final point. And that might be this--
what if you have an artery? So instead of
balloons and bubbles, let's talk about blood
vessels for just a second. What if you had an
artery, like that? And here's my artery. And you decide that you want
to block it off on one end, maybe with your hand, like this. And here's your hand
blocking it off. And let's say you do the
exact same thing with a vein. You decide you want
to take a vein, and block it off on one end. I'm trying to draw these
two to be the same size. So if they look different, then
please assume, for the moment, that they're the same
size, same length. Block it off. So that end is blocked
off with your hand, and nothing can leak out, right? So you only have one open end. And now let's assume that
you cover up this end. Let's say you cover it up. And you have just one
tiny opening here. You cover up the vein. You do the same thing. You have one tiny opening here. And this opening--
let's have it go down, so it looks the same-- this
opening is to a bicycle pump. I know this is
sounding very strange. Why in the world would
you have a bicycle pump attached to an artery or a vein? Well, you'll see
in just a second. Here's my bicycle pump. And I'm going to actually
pump up my artery and pump up my vein
much the same way that I did before with the
balloon and the bubble. And you're going to
start seeing some really interesting parallels, I think. So let's say I
pump up the artery. Immediately what happens? Well, if I put a certain
amount of pressure in there, let's say I put the
large amount of pressure that I had put in the balloon. Well, I'm going to get something
like this, where this artery is going to start swelling up. And this goes away. So now, my artery
looks a little fat, like a plump little sausage. And if I give that same amount
of large pressure to the vein, it's going to do
something like this. It's going to get enormous. And I have to erase these
little lines to make it clear that my vein is getting huge. So with a little
bit of pressure, the artery gets a
little bit bigger. But then a vein
gets a lot bigger. So with the same
amount of pressure, you see a difference
in the volume. And this is actually a
critical point, right? Because the artery and the
vein are really behaving just like the balloon and the bubble. And it's actually
very, very similar. So if I was to make a volume
pressure loop with this, I could actually erase the
word balloon and bubble. And really, replace
them completely with artery and vein. I could just write the
words artery and vein. And essentially, they
would be behaving this way. Artery up here,
artery over here, and then vein in
the other two spots. So you can now see
that the artery has lower compliance
than a vein, and higher elastance
than a vein. And now, just speaking
to the compliance issue, imagine that you had
a really rigid iron pipe, something
completely solid that's not going to budge,
no matter what you do. Well, for that solid
pipe, you'd actually get something like this. You would have even
less compliance. So if you're ever thinking
about the issue of compliance-- and we talk about stiffness--
think about these curves, and the fact that
where the slope is tells you how
complaint something is, and that arteries
are going to be more compliant than a
stiff pipe, certainly, but less compliant
than the veins.